Premenstrual Syndrome (PMS) may have unique physiological underpinnings which make it of considerable interest to biological psychiatry. In pilot studies, we have found that phototherapy and sleep deprivation have marked therapeutic effects in PMS patients. The aims of this proposal are first, to validate the clinical efficacy of these treatments and second, to test hypotheses about their possible mechanisms of action. One hypothesis that we will test is that certain circadian rhythms may be phase-advanced relative to the sleep-wake cycle in some patients with PMS, and that phototherapy and sleep deprivation, by correcting this disturbance, produce clinical remission. We propose 3 studies: In Study I, we will contrast circadian hormones in PMS patients and control subjects. In Study II we will treat PMS patients with either morning bright light (which advances circadian rhythms), evening bright light (which delays circadian rhythms), or with evening dim light (which serves as a placebo control). In Study III, we will contrast late-night partial sleep deprivation (phase delay of sleep) in PMS patients. Our pilot data suggest that PMS patients respond preferentially to evening bright light and to late-night partial sleep deprivation, which is consistent with a phase-advance hypothesis. Since these interventions may be acting through mechanisms other than shifting circadian phase, we will examine alternative theories that might explain the beneficial effects of these treatments. Both phototherapy and sleep deprivation alter TSH and prolactin, hormones implication in the pathogenesis of PMS. Therefore, we will investigate effects of these treatments on circadian and endocrine systems. Thus phototherapy and sleep deprivation may serve not only as clinical probes to test our experimental hypotheses but also as potential alternatives to the pharmacologic management of PMS.